Phycobiliproteins are currently being used as fluorescent markers in many aspects of immunodetection of antigens (e.g. flow cytometry). The currently available phycobiliproteins all exceed 100 kDa molecular weight. A whole class of phycobiliproteins have not been used for this purpose, those that are produced by the cryptomonads. These vary in molecular weight, but all are considerably less than 100 kDa. This proposal seeks to explore the utility of these compounds as fluorescent markers. It proposes to culture at least six different cryptomonads that cover the full range of phycobiliproteins produced by this group of algae. These will be lysed and the pigments extracted and purified to homogeneity. The pigments will be characterized as to their spectrophotometric characteristics and molecular weights. They will be conjugated to avidin or streptavidin and the conjugate tested for stability. The stable conjugates will be given to our consultant for testing in flow cytometry experiments.